Master alloy composition for producing gold alloys and gold alloy

ABSTRACT

A master alloy composition for producing gold alloys with innovative refiners system comprising iridium (Ir): 0.01÷0.8% by weight, ruthenium (Ru): 0.002÷0.9% by weight, rhodium (Rh): 0.002÷0.8% by weight, and copper (Cu): 20÷99.965% by weight, wherein iridium (Ir), ruthenium (Ru) and rhodium (Rh) are the grain refiners.

TECHNICAL FIELD

The present invention concerns a master alloy composition for producinggold alloys with innovative refiners system.

Furthermore, the current invention concerns a gold alloy comprising theaforesaid master alloy composition and used to produce precious jewelry,goldsmith, costume jewelry items (or jewels), coins and/or medals, boththrough a micro-casting process and through a mechanical working.

PRIOR ART

Usefulness of grain refiners as improving chemical elements of theperformances of gold alloys as a whole has been long known in producinggoldsmith and/or jewelry alloys. In particular, main benefits observedby reducing the size of the crystalline grain (refining) in gold alloyswhich follows the introduction of these refiners may be summarized asfollows:

-   -   improvement of physico-mechanical properties in general, in        particular deformability and elongation (physical properties        which can be summarized in the term “ductility” or ability to        withstand plastic deformation);    -   increase of the resistance to corrosion understood, for example,        as decrease in the release of nickel in white gold alloys or as        resistance to acidic emptying solutions in the processes of        production of hollow objects (crimped process, hollow tube,        etc.).

Among the better known, used and most effective grain refiners for goldalloys, iridium (Ir) and ruthenium (Ru) are included.

The same Applicant has described, in European Patent applicationpublished with N. EP1266974 A1, master alloys compositions to obtaingold alloys comprising at least (percentages by weight): iridium ≦0.4%,germanium ≦4% and copper for the difference to 100%. Said compositionsmay also include silver ≦72%, nickel ≦41%, zinc ≦25%, ruthenium ≦0.96%.These compositions, due to the germanium that is present in particularas fluidifying element, possess excellent fluidity in the molten stateand reduced tendency to oxidation even in absence of silicon and also,thanks to the small size of the crystalline grain, are normally able tonot require the use of other refining elements.

As it is well known, iridium (Ir) is a transition metallic elementbelonging to the so-called platinum group metals (PGMs, otherwise alsoknown as platinoids): it has atomic number equal to 77, molecular weightequal to 192 and melts at 2,466° C.

Being a precious element, the cost of this grain refiner is particularlyhigh (about 26÷28

/g, at the time of filing of the present patent application).

Even ruthenium (Ru) is a transition metallic element of the group ofplatinoids: it possesses atomic number equal to 44, molecular weightequal to 101 and melts at 2,334° C. Its cost, however, is considerablylower than that one of iridium (about 2.5÷3

/g at the time of filing of the present patent application).

Since both of these metallic elements have a high melting point and havelimited solubility in gold, it is conceivable that they are alreadypresent as precipitates (separated compounds, because little soluble ina given liquid solution) upon reaching the liquidus temperature of thegold alloy (including fine gold and master alloy), acting as“impurities” or nucleation (or crystallization) centres for theformation and growth of the crystalline grains.

Their addition in the gold alloys or master alloys for producing thefirst ones is carried out in small amounts, generally not exceeding afew hundred of parts per million (ppm) on the final gold alloy.

Furthermore, the established practice commonly followed and the currentstate of the art in the field of production of gold alloys provides thatthese crystalline grain refiners are added individually, never incombination each other, therefore addition of iridium (Ir) is entirelyalternative to addition of ruthenium (Ru).

The addition of only iridium (Ir) or, alternatively, of only ruthenium(Ru) in a master alloy (or in a gold alloy using such a master alloy)involves a significant but still even presumably improvable reduction inthe sizes of the crystalline grain compared to those ones of a goldalloy missing these refiners, although the reduction which can beobtained with the addition of iridium (Ir) is greater than that oneachievable with the addition of ruthenium (Ru).

Such a situation, according to which the iridium (Ir) is preferable tothe ruthenium (Ru) as grain refiner in terms of the improvement of themechanical properties of the alloy, however, must be weighted at thelight of the significantly higher commercial cost of the first one thanthe second one, which however makes not always convenient its use.

It follows that, in the field concerned, the need to use or addcrystalline grain refiners of master alloys or related gold alloys isnow strongly felt which are able to further reduce the sizes of thecrystalline grain of the gold alloy, thus resulting in a markedimprovement of the physical-mechanical properties (in particular,ductility) of the alloy compared to equivalent alloys of known typeprovided with refiners.

At the same time, at the state of the art the need to use refiners whichhave not only high performances in terms of the mechanical features butalso able to affect the production costs of the gold alloy to a lesserextent than the refiners used in the prior art is felt.

In short, at the current state of the technique of the field of the forjewelry and/or goldsmith alloys a need to produce a master alloycomposition for the production of gold alloys remains which exploits arefiners system alternative to that one constituted by the single use ofthe most widespread refiners, that is iridium (Ir) and ruthenium (Ru),while trying to exploit or enhancing the merits of both the latter.

PURPOSES AND BRIEF DESCRIPTION OF THE INVENTION

Starting, therefore, from the knowledge of the drawbacks mentioned aboveof the current state of the art, the present invention seeks to giveconcretely solution to them.

In particular, primary purpose of the present invention is to provide amaster alloy composition for the production of gold alloys which, byusing a special and innovative system of refiners, allows to get sizesof the crystalline grain of the gold alloys themselves better than thoseones of equivalent gold alloys of known type, including refiners.

It is a second purpose of the invention to improve thephysical-mechanical properties, in particular ductility, of a gold alloycompared to similar gold alloys of the known technique.

It is another purpose of the present invention to devise a master alloythat provides a refiners system cheaper than that one of similar knownmaster alloys, degree of crystalline grain refining reached being equal.

It is a last but not least purpose of the invention to make available agold alloy comprising refiners which, generally, while achieving theabove purposes in terms of mechanical performance, presents a cost lowerthan that one of prior art gold alloys equivalent to it.

During several laboratory tests, the Applicant has surprisingly foundthat a system of crystalline grain refiners for gold alloys whereiridium (Ir), ruthenium (Ru) and rhodium (Rh) are added simultaneouslyin the master alloy, then combined by fusion with fine gold to form thegold alloy, is quite beneficial and effective and able to reach thepurposes set above. The invention, indeed, highlights how the combineduse of iridium (Ir), ruthenium (Ru) and rhodium (Rh) causes a synergiceffect of the grain refining properties, and related properties, bythese refining metals, in respect to the separated and alternative useof only iridium (Ir) and ruthenium (Ru) in a given master alloycomposition, as it typically happens in prior art. Even more: such asynergic effect is associated with an overall reduction of the cost ofthe refiners used in the master alloy, because the refining systemcomposed of iridium (Ir), ruthenium (Ru) and rhodium (Rh) allows to geta qualitative level of the physico-mechanical properties listed aboveeven better than that one of the known gold alloys but withoutincreasing the content of iridium (Ir), as said metal significantly andnotoriously more expensive than ruthenium (Ru).

On the other hand, the combination of refiners according to thetechnical concept expressed by the current invention surprisingly allowsto exploit the rhodium (Rh) as innovative and new grain refiner (neverused in the prior art for similar purposes), without causing significantincreases of cost since it is added in small quantities (less than 1%).

As known, rhodium (Rh) is a transition metallic element of the group ofplatinoids: it has atomic number equal to 45, molecular weight equal102.9 and melts at 1,964° C. Its cost, very high in the past, hasdrastically declined in recent times (about 30

/g at the time of filing of the present patent application).

In detail, the combination of a date, however small, amount by weight ofruthenium (Ru) and rhodium (Rh) to iridium (Ir)—without changing thequantity of the latter—surprisingly and advantageously involves a notnegligible reduction of the crystalline grain size of the gold alloy andan equally noticeable increase in the ductility of the same.

Said purposes are achieved by a master alloy composition for theproduction of gold alloys with innovative refiners system and a goldalloy using such a master alloy composition, respectively according tothe appended claims 1 and 12, as hereinafter referred for the sake ofexhibition brevity.

Integral part of the invention is also the use of iridium (Ir),ruthenium (Ru) and rhodium (Rh) as refiners in the production of amaster alloy composition for the production of gold alloys, according toclaim 13 attached, as hereinafter referred for the sake of exposurebrevity.

Object of the present invention is also the use of iridium (Ir),ruthenium (Ru) and rhodium (Rh) as synergic refiners of the crystallinegrain of gold alloys according to claim 14 attached, as stillhereinafter referred for the sake of exhibition brevity.

It is, therefore, a first objective of the present invention, possiblyindependent and usable autonomously with respect to the other aspects ofthe invention, a master alloy composition for the production of goldalloys with innovative refiners system, represented particularly by thesimultaneous presence of iridium (Ir), ruthenium (Ru) and rhodium (Rh)as refiners of the crystalline grain size of the final gold alloyobtained through such a master alloy composition.

It is a second purpose of the invention a master alloy composition forthe production of gold alloys, comprising simultaneously iridium (Ir),ruthenium (Ru) and rhodium (Rh), able to improve, compared to the knowntechnique, the mechanical properties, and in particular the ductility,of the final gold alloy obtained through such a master alloycomposition.

It is, therefore, another purpose of the present invention, possiblyindependent and usable autonomously with respect to the other aspects ofthe invention, a master alloy composition for the production of goldalloys, comprising simultaneously iridium (Ir), ruthenium (Ru) andrhodium (Rh), able to improve, compared to the prior art, the propertiesof resistance to corrosion—for example by reducing the release of nickelin white gold alloys—of the gold alloy obtained through such a masteralloy composition.

It is, therefore, another purpose of the invention, possibly independentand usable autonomously in relation to the other aspects of theinvention, the combined and simultaneous use of iridium (Ir), ruthenium(Ru) and rhodium (Rh) as refiners in the production of a master alloycomposition for the production of gold alloys.

It is, then, a further purpose of the invention, possibly independentand usable autonomously in relation to the other aspects of theinvention, the combined and simultaneous use of iridium (Ir), ruthenium(Ru) and rhodium (Rh) as synergic crystalline grain refiners of goldalloys.

Other technical features of detail of the master alloy composition forthe production of gold alloys with innovative refiners system, and thecorresponding gold alloy, as well as the simultaneous use of iridium(Ir), ruthenium (Ru) and rhodium (Rh) for the production of a masteralloy composition, and related gold alloy, according to the presentinvention, are described in the corresponding dependent claims.

The claims, hereinafter specifically and concretely defined, areconsidered an integral part of the present description.

DESCRIPTION OF THE FIGURES

Further features and specificities of the present invention will appearto a greater extent from the detailed description which follows,relating to preferred embodiments of the master alloy composition, goldalloy and uses claimed herein by exclusive, given by indicative andillustrative, but not limitative, way with reference to the encloseddrawing tables, also provided only by way of example, in which the FIGS.1-3 are three distinct images of the section of a master alloycomposition of the invention, captured using a backscattered electronsbeam (QBSD) of an electronic scanning microscope equipped with amicroprobe (SEM/EDX), at three different levels of enlargement (680×,2080× and 5670×, respectively).

DETAILED DESCRIPTION OF THE INVENTION

While the invention is susceptible to various alternative modificationsand implementations, some embodiments thereof will be described below indetail, in particular by means of some illustrative examples.

It should be understood, however, that there is no intention to limitthe present invention to the specific embodiments described but, on thecontrary, the invention itself intends to cover all the furtheralternative and equivalents modifications and implementations that fallwithin the scope of protection as defined in the appended claims.

In the following description, therefore, use of “for example”, “etc.”and “or” indicates a non-exclusive alternatives without any limitation,unless otherwise stated.

Use of the term “also” means “among which, but not limiting to,” unlessotherwise indicated. In accordance with the invention, the master alloycomposition for the production of gold alloys with innovative refinerssystem includes:

-   -   iridium (Ir): 0.01÷0.8% by weight;    -   ruthenium (Ru): 0.002÷0.9% by weight;    -   rhodium (Rh): 0.002÷0.8% by weight;    -   copper (Cu): 20÷99.965% by weight,        wherein iridium (Ir), ruthenium (Ru) and rhodium (Ru) are added        as the refining elements of the crystalline grain.

In particular, the percentage by weight of iridium (Ir) is preferably inthe range between 0.03% and 0.17%.

Still more in particular, the percentage by weight of iridium (Ir) is inthe range between 0.03% and 0.06% for yellow gold alloys, while it is inthe range between 0.1% and 0.16% for white gold alloys.

Preferably, the weight percentage of ruthenium (Ru) is in the rangebetween 0.003% and 0.09%.

In further preferred but not exclusive manner, the percentage by weightof ruthenium (Ru) is in the range between 0.0045% and 0.04% for yellowgold alloys, while it is in the range between 0.01% and 0.08% for whitegold alloys.

Preferably, also, the percentage by weight of rhodium (Rh) is in therange between 0.05% and 0.15% and for example it is equal to 0.1% byweight.

Preferably but not necessarily, the master alloy composition concernedfurther comprises zinc (Zn): 1÷25% by weight.

In a preferred but not binding way, the percentage by weight of zinc(Zn) is in the range between 1% and 18%.

Even more in detail, the percentage by weight of zinc (Zn) is in therange between 1% and 12% for yellow gold alloys and in the range between7% and 14% in case of white gold alloys; this depending on the title(carat) of the final gold alloy to be obtained.

As mentioned above, it is also possible to provide master alloycompositions deprived of zinc (so-called “zinc-free”), as it will beshown in the examples below; the absence of this element, while notcompromising the mechanical features and resistance to corrosion nor theperformances in terms of color and workability, especially in case ofyellow or red alloys, allows to stabilize the weight of the casting andconsequently the title of the alloy.

In case of yellow gold alloys, preferably, the master alloy compositionof the invention further includes silver (Ag): 20÷64% by weight.

If, instead, the final alloy to be produced provides white gold,preferably the master alloy composition further comprises nickel (Ni):5÷40% by weight.

As already mentioned, another integral aspect of the invention concernsa gold alloy with innovative refiners system which includes:

-   -   gold (Au): 333.33‰ (8 k)÷958.33‰ (23 k) by weight;    -   a master alloy composition as just identified and described, for        the remaining part by weight.

According to a preferred embodiment of the gold alloy of the invention,the percentage by weight of gold (Au) is equal to 750‰ (18 k) and thepercentage by weight of the master alloy composition is equal to 250‰.

In accordance with another preferred and alternative embodiment of thegold alloy of the invention, the percentage by weight of gold (Au) isequal to 585‰ (14 k) and the percentage by weight of the master alloycomposition is equal to 415‰.

By way of preferred but not exclusive example, the above gold alloy ofthe invention provides that the metals of the master alloy compositionare bonded together in order to form an intermediate, separated anddistinct, compound, subsequently combined to the fine gold (Au) toobtain precisely the final gold alloy.

This does not exclude, however, that in other embodiments of the goldalloy of the invention, the metals of the master alloy composition arebonded directly to gold (Au) during the production phase of the finalgold alloy, i.e. without creating an intermediate compound.

Another aspect of the present invention relates to the use of iridium(Ir), ruthenium (Ru) and rhodium (Rh) as refiners in the production of amaster alloy composition for the production of gold alloys, whereiniridium (Ir), ruthenium (Ru) and rhodium (Rh) are used simultaneouslyand in combination each other.

A further aspect of the present invention refers to the use of iridium(Ir), ruthenium (Ru) and rhodium (Rh) as synergic refiners of thecrystalline grain of gold alloys, wherein, again, iridium (Ir),ruthenium (Ru) and rhodium (Rh) are used simultaneously and incombination each other.

Some preferred but not limiting examples of the master alloycomposition, and the resulting gold alloy with innovative refinerssystem, object of the invention, are described below.

Example 1 750‰ Yellow Gold Alloy

Table I below compares four master alloy compositions with differentrefining systems of the crystalline grain, three of these master alloycompositions are of known and traditional type (indicated with thereference “A”, “C” and “D”), while the remaining master alloycomposition is designed according to the teachings of the invention(reference “B” in bold). It is also stated precisely that, in thefollowing Table I, the term “bal” for copper (Cu) stands for “balanced”and indicates that this element is present in an amount by weightnecessary to complete the master alloy composition to 100%.

In the lower part of Table I the main physico-mechanical propertiesrelated to the corresponding gold alloy, having in this case a title of750‰ (18 k), comprising the directly above master alloy compositionreported in Table I, are reported.

Master alloy compositions “A” and “C” of the prior art provide differenttypes of refiners inserted individually, while the master alloycomposition “B” of the invention provides three different types ofrefiners inserted simultaneously.

The master alloy composition indicated by the reference “D” is, instead,a traditional version without any kind of grain refiner.

It can be clearly seen that the composition of the master alloy “B”according to the invention, in which the triple refiner system(Ir+Ru+Rh) is inserted holds crystalline grain having sizes about 35%lower than the refined alloy only with Iridium (Ir).

It is also stressed how the triple refiner system (Ir+Ru+Rh) produce asignificant improvement in the ductility of the alloy (indicated with A%), amounting to 22%.

TABLE I Composition (% by weight on master alloy) A B C D Zn 9 9 9 9 Ag45 45 45 45 Ir 0.04 0.04 — — Ru — 0.0045 0.0045 — Rh — 0.1 — — Cu balbal bal bal Measured properties (750%₀ - 18k gold alloy) Grain (μm) 12070 85 700 A% 38 47 39 38

In FIGS. 1, 2 and 3 attached, referring to the sample of master alloycomposition “B” of the present invention shown in Table I, it can beobserved some surveys carried out by means of backscattered electronsbeam (QBSD) with electronic scanning microscope with microprobe(SEM/EDX), at three different levels of enlargement (FIG. 1=680x; FIG.2=2080x; FIG. 3=5670x).

From the images of these FIGS. 1-3 at the origin of the dendrites, thepresence of a nucleus consisting of elements of high molecular weight(light color) appears clearly visible.

Example 2 750‰ Yellow Gold Alloy

The second favourite, although not binding, example of master alloycomposition (and corresponding gold alloy) of the invention presentedherein is derived from Table II below, which compares three masteralloys compositions having different grain refining systems. Inparticular, Table II shows two master alloy compositions of the knownand traditional type, (indicated respectively with the reference “E” and“G”, each having a single refiner different from that one of the other),and a master alloy composition designed according to the concept of theinvention (indicated with the reference “F” in bold), i.e. with triplerefiner. “Bal” term for copper (Cu) used in Table II means again“balanced” and indicates that this element is present in an amount byweight necessary to complete the master alloy composition to 100%.

Moreover, at the bottom of Table II the main physico-mechanicalproperties related to the corresponding 750‰ gold alloy are shown.

TABLE II Composition (% by weight on master alloy) E F G Zn 8 8 8 Ag 4747 47 Ir 0.04 0.04 — Ru — 0.04 0.04 Rh — 0.04 — Cu bal bal Bal Measuredproperties (750%₀ - 18k gold alloy) A% 29 34 30

Also in this case it can be observed how by including in the masteralloy composition the triple refiner system according to the invention(iridium (Ir)+ruthenium (Ru)+rhodium (Rh)) produces an increase ofductility (parameter A %) more than proportional to the addition of theindividual refiners in a given master alloy composition.

Example 3 750‰ White Gold Alloy

Another important novelty introduced by the invention is the ability ofthe crystalline grain refining system—that involves the simultaneousaddition of iridium (Ir), ruthenium (Ru) and rhodium (Rh)—to increasethe properties of resistance to corrosion in white gold alloys.

It follows that in white gold alloys which provide the simultaneouspresence of iridium (Ir), ruthenium (Ru) and rhodium (Rh) as refiners ithas been observed a further reduction of the values of nickel releasecompared to what has been observed in alloys of equal composition inwhich the grain refiners, such as typically iridium (Ir) and ruthenium(Ru), are included as individual elements, not in combination.

Such a property is particularly important when it is considered thatfrom the next April 2013 will come into force the new revisionEN1811:2011 of the European standard on the nickel release, whichprovides the adoption of limits of nickel release by goldsmith, jewelryand costume jewelry articles much more restrictive than the currentones.

As known, nickel is a low cost metal, used in jewelry as whiteningelement of gold.

The problem of allergies (contact dermatitis) caused by the release ofnickel on the skin of people who are particularly subject has been wellknown for many years. The public has shown an increasing level ofconcern about the issue of the release of nickel, to the point ofpushing the European Union to adopt a Community regulatory directive onthe use of such a metal, formed in particular by the legislation on thenickel EN1811 whose first publication dates back to 1994.

With the entry into force of the new revision of the regulationEN1811:2011, nickel release values actually determined shall not exceedthe values of 0.28 g/cm²/week—for objects in long contact with theskin—and 0.11 g/cm²/week—for objects to be inserted into pierced partsof the body—.

Compared to the previous version of the legislation, the new standardEN1811:2011 de facto determines the reduction of the maximum releaselimit of more than 18 times with respect to the release limit allowed bythe previous version of the legislation concerned.

The entry into force of the new standard will result, therefore, inheavy restrictions with respect to the availability of nickel-basedalloys which can be still used by manufacturers.

The metallurgical implications that will follow the introduction of thenew standard are extremely important.

That being stated, the present invention demonstrates that through theuse of the triple refiner system iridium (Ir), ruthenium (Ru) andrhodium (Rh) release values can be further reduced, leading them to asafe range, well below the maximum limit allowed by the new regulationsEN1811:2011, as shown by table III below.

In such a Table III, comparative tests among master alloy compositionswith different types of crystalline grain refining systems are shown.

More in detail, master alloy compositions indicated with “H” and “L” areof traditional type and each provide a single refiner (either iridium(Ir) or ruthenium (Ru), alternative each other), while the master alloycomposition indicated with “I” (highlighted in bold), is designedaccording to the invention, using a triple refiner system (Ir+Ru+Rh).

The term “bal” for copper (Cu) always stands to shorten the word“balanced” and provides that this element is present in an amount byweight necessary to complete the master alloy composition to 100%.

The lower part of Table III shows the main physico-mechanical propertiesrelated to the corresponding white gold alloy, having in the specificcase a title equal to 750‰ (18 k).

The example of Table III compares the crystalline grain sizes, and therelated nickel release values, of white gold alloys having a masteralloy composition with single grain refiner (only iridium (Ir) for themaster alloy composition “H” and only ruthenium (Ru) for the masteralloy composition “L”), with the relevant parameters of white goldalloys having a master alloy composition with triple refiner system,comprising, in particular, iridium (Ir), ruthenium (Ru) and rhodium(Rh)) (master alloy composition “I”).

It can be clearly appreciated the synergic effect determined by thesimultaneous addition of the three refiners iridium (Ir), ruthenium (Ru)and rhodium (Rh) [cf. master alloy composition “I”] not only in refiningthe crystalline grain but also in reducing the nickel release value,which is conveniently much lower than the limit prescribed by the newstandard EN1811:2011 (0.28 g/cm²/week), with the obvious advantages thatthis entails.

Table III Composition (% by weight on master alloy) H I L Zn 16 16 16 Ni17 17 17 Ir 0.14 0.14 — Ru — 0.04 0.04 Rh — 0.1 — Cu bal bal balMeasured properties (750%₀ - 18k gold alloy) Grain (μm) 185 ± 15 64 ± 1795 ± 20 Nichel release (μg/cm²/week) 0.203 0.065 0.103

Example 4 750‰ White Gold Alloy

Even Table IV below shows comparative tests, carried out by theApplicant, including alloys compositions with different grain refiningsystems, intended to form white gold alloys.

More specifically, master alloy compositions indicated with “M” and “O”are of conventional and well known type, each providing a single refiner(either iridium (Ir) or ruthenium (Ru), alternative to each other),while master alloy composition indicated with “N” (highlighted in bold)is designed according to the invention, using simultaneously iridium(Ir), ruthenium (Ru) and rhodium (Rh) as refining elements of thecrystalline grain (triple refiner system).

As usual in this paper, the term “bal” for copper (Cu) abbreviates theword “balanced” and indicates that this element is present in an amountby weight necessary to complete the master alloy composition to 100%.

The lower part of the table shows the main physical and mechanicalproperties (grain size and ductility) referred to the corresponding 750‰(18 k) gold alloy.

In the example of Table IV the sizes of crystalline grain, and theirnickel release values, of white gold alloys whose corresponding masteralloy includes a single grain refiner (only iridium (Ir), master alloycomposition “M”, and only ruthenium (Ru), master alloy composition “O”),are compared with the same parameters of white gold alloys whose relatedmaster alloy composition “N” includes three grain refiners, in this caseiridium (Ir), ruthenium (Ru) and rhodium (Rh).

It should be clearly observed the synergic effect of the triple refinersystem, particularly iridium (Ir), ruthenium (Ru) and rhodium (Rh),[master alloy composition indicated with “N”] in refining thecrystalline grain and reducing the nickel release value that is,advantageously, well below the limit prescribed by the new standardEN1811:2011 (0.28 g/cm²/week).

TABLE IV Composition (% by weight on master alloy) M N O Zn 17 17 17 Ni18.5 18.5 18.5 Ir 0.16 0.16 — Ru — 0.08 0.08 Rh — 0.08 — Cu bal bal balMeasured properties (750%₀ - 18k gold alloy) Grain (μm) 170 ± 19 60 ± 21102 ± 20 Nichel release (μg/cm²/week) 0.215 0.055 0.120

Example 5 750‰ White Gold Alloy

It is, finally, considered useful to provide, in Table V below, someadditional comparative data between two traditional master alloycompositions (respectively indicated with “P” and “R”) and a masteralloy composition according to the present invention, indicated with“Q”. As usual, the term “bal” for copper (Cu) abbreviates the word“balanced” and indicates that it is present in an amount by weightuseful to complete to 100% the master alloy composition.

TABLE V Composition (% by weight on master alloy) P Q R Ir 0.15 0.150.15 Ru — 0.1 0.1 Rh — 0.1 — Cu bal bal bal Measured properties (750%₀ -18k gold alloy) Grain (μm) 140 70 115

As it can be easily noted, the composition according to the presentinvention allows to get a crystalline grain having a size reduced up toabout the half compared to that one of the traditional compositions ofthe prior art, this resulting from the simultaneous and combined use ofiridium, ruthenium and rhodium.

On the basis of the description just given, it is understood, therefore,that the master alloy composition for the production of gold alloys withinnovative refiners system, the gold alloy using such a master alloycomposition and the uses of the present invention reach the purposes andachieve the advantages previously mentioned.

It is, finally, clear that several other changes could be made to theinvention concerned, without departing from the principle of noveltyintrinsic in the inventive idea expressed herein, as it is clear that,in the practical implementation of the invention, materials, shapes andsizes of the illustrated details could be changed, as needed, andreplaced with others technically equivalent.

Where the constructive features and techniques mentioned in thefollowing claims are followed by reference numbers or signs, thosereference signs have been introduced with the sole objective ofincreasing the intelligibility of the claims themselves and thereforethey have no limiting effect on the interpretation of each elementidentified, by way of example only, by these reference signs.

1. Master alloy composition for producing gold alloys with innovativerefiners system comprising: iridium (Ir): 0.01 to 0.8% by weight;ruthenium (Ru): 0.002 to 0.9% by weight; rhodium (Rh): 0.002 to 0.8% byweight; copper (Cu): 20 to 99.965% by weight.
 2. Master alloycomposition according to claim 1, wherein the iridium (Ir) weightpercentage is in the range between 0.03% and 0.17%.
 3. Master alloycomposition according to claim 2, wherein the iridium (Ir) weightpercentage is in the range between 0.03% and 0.06% for yellow goldalloys and in the range between 0.1% and 0.16% for white gold alloys. 4.Master alloy composition according to claim 1, wherein the ruthenium(Ru) weight percentage is in the range between 0.03% and 0.09%. 5.Master alloy composition according to claim 4, wherein ruthenium (Ru)weight percentage is in the range between 0.0045% and 0.04% for yellowgold alloys and in the range between 0.01% and 0.08% for white goldalloys.
 6. Master alloy composition according to claim 1, wherein therhodium (Rh) weight percentage is in the range between 0.05% and 0.15%.7. Master alloy composition according to claim 1, further comprisingzinc (Zn) wherein the zinc(Zn) weight percentage is in the range between1 and 25%.
 8. Master alloy composition according to claim 7, wherein thezinc (Zn) weight percentage is in the range between 1% and 18%. 9.Master alloy composition according to claim 8, wherein the zinc (Zn)weight percentage is in the range between 1% and 12% for yellow gold andin the range between 7% and 14% white gold alloys.
 10. Master alloycomposition according to claim 1, further comprising silver (Ag) whereinthe silver (Ag) weight percentage is in the range between 20 and 64%.11. Master alloy composition according to claim 1, further comprisingnickel (Ni) wherein the nickel weight percentage is in the range between5 and 40%.
 12. Gold alloy with innovative refiners system comprising:gold (Au): 333.33‰ (8 k) to 958.33‰ (23 k) by weight; master alloycomposition according to claim 1, for the remaining part by weight.13-14. (canceled)
 15. A method of making a gold alloy which comprisesadding an amount of a master alloy composition of claim 1 to gold toform a gold alloy having 333.33‰ (8 k) to 958.33‰ (23 k) by weight ofgold.